Method and apparatus for processing video signal

ABSTRACT

A method for decoding a video according to the present invention may comprise: determining a motion vector precision of a current block, generating a motion vector candidate list of the current block, obtaining a motion vector prediction value of the current block from the motion vector candidate list, determining whether a precision of the motion vector prediction value is identical to a motion vector precision of the current block, scaling the motion vector prediction value according to the motion vector precision of the current block, when the precision of the motion vector prediction value is different from the motion vector precision of the current block, and obtaining a motion vector of the current block using the scaled motion vector prediction value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.17/015,648 (filed on Sep. 9, 2020), which is a Continuation of U.S.patent application Ser. No. 16/472,849 (filed on Jun. 21, 2019), nowissued as U.S. Pat. No. 10,805,608, which is a National Stage PatentApplication of PCT International Patent Application No.PCT/KR2017/014869 (filed on Dec. 15, 2017) under 35 U.S.C. § 371, whichclaims priority to Korean Patent Application No. 10-2016-0176441 (filedon Dec. 22, 2016), the teachings of which are incorporated herein intheir entireties by reference.

TECHNICAL FIELD

The present invention relates to a method and an apparatus forprocessing video signal.

BACKGROUND ART

Recently, demands for high-resolution and high-quality images such ashigh definition (HD) images and ultra-high definition (UHD) images haveincreased in various application fields. However, higher resolution andquality image data has increasing amounts of data in comparison withconventional image data. Therefore, when transmitting image data byusing a medium such as conventional wired and wireless broadbandnetworks, or when storing image data by using a conventional storagemedium, costs of transmitting and storing increase. In order to solvethese problems occurring with an increase in resolution and quality ofimage data, high-efficiency image encoding/decoding techniques may beutilized.

Image compression technology includes various techniques, including: aninter-prediction technique of predicting a pixel value included in acurrent picture from a previous or subsequent picture of the currentpicture; an intra-prediction technique of predicting a pixel valueincluded in a current picture by using pixel information in the currentpicture; an entropy encoding technique of assigning a short code to avalue with a high appearance frequency and assigning a long code to avalue with a low appearance frequency; etc. Image data may beeffectively compressed by using such image compression technology, andmay be transmitted or stored.

In the meantime, with demands for high-resolution images, demands forstereographic image content, which is a new image service, have alsoincreased. A video compression technique for effectively providingstereographic image content with high resolution and ultra-highresolution is being discussed.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and anapparatus for efficiently performing inter prediction for anencoding/decoding target block in encoding/decoding a video signal.

An object of the present invention is to provide a method and anapparatus for variably determining a motion vector precision inencoding/decoding a video signal.

An object of the present invention is to provide a method and anapparatus for compensating a difference between motion vector precisionsof blocks by comparing the motion vector precisions of the blocks.

The technical objects to be achieved by the present invention are notlimited to the above-mentioned technical problems. And, other technicalproblems that are not mentioned will be apparently understood to thoseskilled in the art from the following description.

Technical Solution

A method and an apparatus for decoding a video signal according to thepresent invention may determine a motion vector precision of a currentblock, generate a motion vector candidate list of the current block,obtain a motion vector prediction value of the current block from themotion vector candidate list, determine whether a precision of themotion vector prediction value is identical to a motion vector precisionof the current block, scale the motion vector prediction value accordingto the motion vector precision of the current block when the precisionof the motion vector prediction value is different from the motionvector precision of the current block, and obtain a motion vector of thecurrent block using the scaled motion vector prediction value.

A method and an apparatus for encoding a video signal according to thepresent invention may determine a motion vector precision of a currentblock, generate a motion vector candidate list of the current block,obtain a motion vector prediction value of the current block from themotion vector candidate list, determine whether a precision of themotion vector prediction value is identical to a motion vector precisionof the current block, scale the motion vector prediction value accordingto the motion vector precision of the current block when the precisionof the motion vector prediction value is different from the motionvector precision of the current block, and obtain a motion vector of thecurrent block using the scaled motion vector prediction value.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the motion vector precision of thecurrent block is determined from a motion vector precision setcomprising a plurality of motion vector precision candidates.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the motion vector precision of thecurrent block is determined based on index information specifying oneamong the plurality of motion vector precision candidates.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, a motion vector difference valuecomprises a prefix part representing an integer part and a suffix partrepresenting a fractional part.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the scaling is performed by a bitshift operation based on a scale ratio between the precision of themotion vector prediction value and the motion vector precision of thecurrent block.

The features briefly summarized above for the present invention are onlyillustrative aspects of the detailed description of the invention thatfollows, but do not limit the scope of the invention.

Advantageous Effects

According to the present invention, an efficient inter prediction may beperformed for an encoding/decoding target block.

According to the present invention, it is possible to determine a motionvector precision variably.

According to the present invention, a motion vector can be derived bycompensating a difference between motion vector resolutions of blocks.

The effects obtainable by the present invention are not limited to theabove-mentioned effects, and other effects not mentioned can be clearlyunderstood by those skilled in the art from the description below.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a device for encoding a videoaccording to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a device for decoding a videoaccording to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of hierarchicallypartitioning a coding block based on a tree structure according to anembodiment of the present invention.

FIG. 4 is a diagram illustrating a partition type in which binarytree-based partitioning is allowed according to an embodiment of thepresent invention.

FIGS. 5A and 5B are diagrams illustrating an example in which only abinary tree-based partition of a predetermined type is allowed accordingto an embodiment of the present invention.

FIG. 6 is a diagram for explaining an example in which informationrelated to the allowable number of binary tree partitioning isencoded/decoded, according to an embodiment to which the presentinvention is applied.

FIG. 7 is a diagram illustrating a partition mode applicable to a codingblock according to an embodiment of the present invention.

FIG. 8 is a flowchart illustrating an inter prediction method accordingto an embodiment of the present invention.

FIG. 9 is a diagram illustrating a process of deriving motioninformation of a current block when a merge mode is applied to a currentblock.

FIG. 10 illustrates a process of deriving motion information of acurrent block when an AMVP mode is applied to the current block.

FIGS. 11 and 12 illustrate mothing vector derivation methods accordingto a motion vector precision of a current block.

MODE FOR INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, and theexemplary embodiments can be construed as including all modifications,equivalents, or substitutes in a technical concept and a technical scopeof the present invention. The similar reference numerals refer to thesimilar element in described the drawings.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.Hereinafter, the same constituent elements in the drawings are denotedby the same reference numerals, and a repeated description of the sameelements will be omitted.

FIG. 1 is a block diagram illustrating a device for encoding a videoaccording to an embodiment of the present invention.

Referring to FIG. 1, the device 100 for encoding a video may include: apicture partitioning module 110, prediction modules 120 and 125, atransform module 130, a quantization module 135, a rearrangement module160, an entropy encoding module 165, an inverse quantization module 140,an inverse transform module 145, a filter module 150, and a memory 155.

The constitutional parts shown in FIG. 1 are independently shown so asto represent characteristic functions different from each other in thedevice for encoding a video. Thus, it does not mean that eachconstitutional part is constituted in a constitutional unit of separatedhardware or software. In other words, each constitutional part includeseach of enumerated constitutional parts for convenience. Thus, at leasttwo constitutional parts of each constitutional part may be combined toform one constitutional part or one constitutional part may be dividedinto a plurality of constitutional parts to perform each function. Theembodiment where each constitutional part is combined and the embodimentwhere one constitutional part is divided are also included in the scopeof the present invention, if not departing from the essence of thepresent invention.

Also, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

The picture partitioning module 110 may partition an input picture intoone or more processing units. Here, the processing unit may be aprediction unit (PU), a transform unit (TU), or a coding unit (CU). Thepicture partitioning module 110 may partition one picture intocombinations of multiple coding units, prediction units, and transformunits, and may encode a picture by selecting one combination of codingunits, prediction units, and transform units with a predeterminedcriterion (e.g., cost function).

For example, one picture may be partitioned into multiple coding units.A recursive tree structure, such as a quad tree structure, may be usedto partition a picture into coding units. A coding unit which ispartitioned into other coding units with one picture or a largest codingunit as a root may be partitioned with child nodes corresponding to thenumber of partitioned coding units. A coding unit which is no longerpartitioned by a predetermined limitation serves as a leaf node. Thatis, when it is assumed that only square partitioning is possible for onecoding unit, one coding unit may be partitioned into four other codingunits at most.

Hereinafter, in the embodiment of the present invention, the coding unitmay mean a unit performing encoding, or a unit performing decoding.

A prediction unit may be one of partitions partitioned into a square ora rectangular shape having the same size in a single coding unit, or aprediction unit may be one of partitions partitioned so as to have adifferent shape/size in a single coding unit.

When a prediction unit subjected to intra prediction is generated basedon a coding unit and the coding unit is not the smallest coding unit,intra prediction may be performed without partitioning the coding unitinto multiple prediction units N×N.

The prediction modules 120 and 125 may include an inter predictionmodule 120 performing inter prediction and an intra prediction module125 performing intra prediction. Whether to perform inter prediction orintra prediction for the prediction unit may be determined, and detailedinformation (e.g., an intra prediction mode, a motion vector, areference picture, etc.) according to each prediction method may bedetermined. Here, the processing unit subjected to prediction may bedifferent from the processing unit for which the prediction method anddetailed content is determined. For example, the prediction method, theprediction mode, etc. may be determined by the prediction unit, andprediction may be performed by the transform unit. A residual value(residual block) between the generated prediction block and an originalblock may be input to the transform module 130. Also, prediction modeinformation, motion vector information, etc. used for prediction may beencoded with the residual value by the entropy encoding module 165 andmay be transmitted to a device for decoding a video. When a particularencoding mode is used, it is possible to transmit to a device fordecoding video by encoding the original block as it is withoutgenerating the prediction block through the prediction modules 120 and125.

The inter prediction module 120 may predict the prediction unit based oninformation of at least one of a previous picture or a subsequentpicture of the current picture, or may predict the prediction unit basedon information of some encoded regions in the current picture, in somecases. The inter prediction module 120 may include a reference pictureinterpolation module, a motion prediction module, and a motioncompensation module.

The reference picture interpolation module may receive reference pictureinformation from the memory 155 and may generate pixel information of aninteger pixel or less then the integer pixel from the reference picture.In the case of luma pixels, an 8-tap DCT-based interpolation filterhaving different filter coefficients may be used to generate pixelinformation of an integer pixel or less than an integer pixel in a unitof a ¼ pixel. In the case of chroma signals, a 4-tap DCT-basedinterpolation filter having different filter coefficient may be used togenerate pixel information of an integer pixel or less than an integerpixel in a unit of a ⅛ pixel.

The motion prediction module may perform motion prediction based on thereference picture interpolated by the reference picture interpolationmodule. As methods for calculating a motion vector, various methods,such as a full search-based block matching algorithm (FBMA), a threestep search (TSS), a new three-step search algorithm (NTS), etc., may beused. The motion vector may have a motion vector value in a unit of a ½pixel or a ¼ pixel based on an interpolated pixel. The motion predictionmodule may predict a current prediction unit by changing the motionprediction method. As motion prediction methods, various methods, suchas a skip method, a merge method, an AMVP (Advanced Motion VectorPrediction) method, an intra block copy method, etc., may be used.

The intra prediction module 125 may generate a prediction unit based onreference pixel information neighboring to a current block which ispixel information in the current picture. When the neighboring block ofthe current prediction unit is a block subjected to inter prediction andthus a reference pixel is a pixel subjected to inter prediction, thereference pixel included in the block subjected to inter prediction maybe replaced with reference pixel information of a neighboring blocksubjected to intra prediction. That is, when a reference pixel is notavailable, at least one reference pixel of available reference pixelsmay be used instead of unavailable reference pixel information.

Prediction modes in intra prediction may include a directionalprediction mode using reference pixel information depending on aprediction direction and a non-directional prediction mode not usingdirectional information in performing prediction. A mode for predictingluma information may be different from a mode for predicting chromainformation, and in order to predict the chroma information, intraprediction mode information used to predict luma information orpredicted luma signal information may be utilized.

In performing intra prediction, when the size of the prediction unit isthe same as the size of the transform unit, intra prediction may beperformed on the prediction unit based on pixels positioned at the left,the top left, and the top of the prediction unit. However, in performingintra prediction, when the size of the prediction unit is different fromthe size of the transform unit, intra prediction may be performed usinga reference pixel based on the transform unit. Also, intra predictionusing N×N partitioning may be used for only the smallest coding unit.

In the intra prediction method, a prediction block may be generatedafter applying an AIS (Adaptive Intra Smoothing) filter to a referencepixel depending on the prediction modes. The type of the AIS filterapplied to the reference pixel may vary. In order to perform the intraprediction method, an intra prediction mode of the current predictionunit may be predicted from the intra prediction mode of the predictionunit neighboring to the current prediction unit. In prediction of theprediction mode of the current prediction unit by using mode informationpredicted from the neighboring prediction unit, when the intraprediction mode of the current prediction unit is the same as the intraprediction mode of the neighboring prediction unit, informationindicating that the prediction modes of the current prediction unit andthe neighboring prediction unit are equal to each other may betransmitted using predetermined flag information. When the predictionmode of the current prediction unit is different from the predictionmode of the neighboring prediction unit, entropy encoding may beperformed to encode prediction mode information of the current block.

Also, a residual block including information on a residual value whichis a different between the prediction unit subjected to prediction andthe original block of the prediction unit may be generated based onprediction units generated by the prediction modules 120 and 125. Thegenerated residual block may be input to the transform module 130.

The transform module 130 may transform the residual block including theinformation on the residual value between the original block and theprediction unit generated by the prediction modules 120 and 125 by usinga transform method, such as discrete cosine transform (DCT), discretesine transform (DST), and KLT. Whether to apply DCT, DST, or KLT inorder to transform the residual block may be determined based on intraprediction mode information of the prediction unit used to generate theresidual block.

The quantization module 135 may quantize values transformed to afrequency domain by the transform module 130. Quantization coefficientsmay vary depending on the block or importance of a picture. The valuescalculated by the quantization module 135 may be provided to the inversequantization module 140 and the rearrangement module 160.

The rearrangement module 160 may rearrange coefficients of quantizedresidual values.

The rearrangement module 160 may change a coefficient in the form of atwo-dimensional block into a coefficient in the form of aone-dimensional vector through a coefficient scanning method. Forexample, the rearrangement module 160 may scan from a DC coefficient toa coefficient in a high frequency domain using a zigzag scanning methodso as to change the coefficients to be in the form of one-dimensionalvectors. Depending on the size of the transform unit and the intraprediction mode, vertical direction scanning where coefficients in theform of two-dimensional blocks are scanned in the column direction orhorizontal direction scanning where coefficients in the form oftwo-dimensional blocks are scanned in the row direction may be usedinstead of zigzag scanning. That is, which scanning method among zigzagscanning, vertical direction scanning, and horizontal direction scanningis used may be determined depending on the size of the transform unitand the intra prediction mode.

The entropy encoding module 165 may perform entropy encoding based onthe values calculated by the rearrangement module 160. Entropy encodingmay use various encoding methods, for example, exponential Golombcoding, context-adaptive variable length coding (CAVLC), andcontext-adaptive binary arithmetic coding (CABAC).

The entropy encoding module 165 may encode a variety of information,such as residual value coefficient information and block typeinformation of the coding unit, prediction mode information, partitionunit information, prediction unit information, transform unitinformation, motion vector information, reference frame information,block interpolation information, filtering information, etc. from therearrangement module 160 and the prediction modules 120 and 125.

The entropy encoding module 165 may entropy encode the coefficients ofthe coding unit input from the rearrangement module 160.

The inverse quantization module 140 may inversely quantize the valuesquantized by the quantization module 135 and the inverse transformmodule 145 may inversely transform the values transformed by thetransform module 130. The residual value generated by the inversequantization module 140 and the inverse transform module 145 may becombined with the prediction unit predicted by a motion estimationmodule, a motion compensation module, and the intra prediction module ofthe prediction modules 120 and 125 such that a reconstructed block canbe generated.

The filter module 150 may include at least one of a deblocking filter,an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion that occurs due toboundaries between the blocks in the reconstructed picture. In order todetermine whether to perform deblocking, the pixels included in severalrows or columns in the block may be a basis of determining whether toapply the deblocking filter to the current block. When the deblockingfilter is applied to the block, a strong filter or a weak filter may beapplied depending on required deblocking filtering strength. Also, inapplying the deblocking filter, horizontal direction filtering andvertical direction filtering may be processed in parallel.

The offset correction module may correct offset with the originalpicture in a unit of a pixel in the picture subjected to deblocking. Inorder to perform the offset correction on a particular picture, it ispossible to use a method of applying offset in consideration of edgeinformation of each pixel or a method of partitioning pixels of apicture into the predetermined number of regions, determining a regionto be subjected to perform offset, and applying the offset to thedetermined region.

Adaptive loop filtering (ALF) may be performed based on the valueobtained by comparing the filtered reconstructed picture and theoriginal picture. The pixels included in the picture may be divided intopredetermined groups, a filter to be applied to each of the groups maybe determined, and filtering may be individually performed for eachgroup. Information on whether to apply ALF and a luma signal may betransmitted by coding units (CU). The shape and filter coefficient of afilter for ALF may vary depending on each block. Also, the filter forALF in the same shape (fixed shape) may be applied regardless ofcharacteristics of the application target block.

The memory 155 may store the reconstructed block or picture calculatedthrough the filter module 150. The stored reconstructed block or picturemay be provided to the prediction modules 120 and 125 in performinginter prediction.

FIG. 2 is a block diagram illustrating a device for decoding a videoaccording to an embodiment of the present invention.

Referring to FIG. 2, the device 200 for decoding a video may include: anentropy decoding module 210, a rearrangement module 215, an inversequantization module 220, an inverse transform module 225, predictionmodules 230 and 235, a filter module 240, and a memory 245.

When a video bitstream is input from the device for encoding a video,the input bitstream may be decoded according to an inverse process ofthe device for encoding a video.

The entropy decoding module 210 may perform entropy decoding accordingto an inverse process of entropy encoding by the entropy encoding moduleof the device for encoding a video. For example, corresponding to themethods performed by the device for encoding a video, various methods,such as exponential Golomb coding, context-adaptive variable lengthcoding (CAVLC), and context-adaptive binary arithmetic coding (CABAC)may be applied.

The entropy decoding module 210 may decode information on intraprediction and inter prediction performed by the device for encoding avideo.

The rearrangement module 215 may perform rearrangement on the bitstreamentropy decoded by the entropy decoding module 210 based on therearrangement method used in the device for encoding a video. Therearrangement module may reconstruct and rearrange the coefficients inthe form of one-dimensional vectors to the coefficient in the form oftwo-dimensional blocks. The rearrangement module 215 may receiveinformation related to coefficient scanning performed in the device forencoding a video and may perform rearrangement via a method of inverselyscanning the coefficients based on the scanning order performed in thedevice for encoding a video.

The inverse quantization module 220 may perform inverse quantizationbased on a quantization parameter received from the device for encodinga video and the rearranged coefficients of the block.

The inverse transform module 225 may perform the inverse transform,i.e., inverse DCT, inverse DST, and inverse KLT, which is the inverseprocess of transform, i.e., DCT, DST, and KLT, performed by thetransform module on the quantization result by the device for encoding avideo. Inverse transform may be performed based on a transfer unitdetermined by the device for encoding a video. The inverse transformmodule 225 of the device for decoding a video may selectively performtransform schemes (e.g., DCT, DST, and KLT) depending on multiple piecesof information, such as the prediction method, the size of the currentblock, the prediction direction, etc.

The prediction modules 230 and 235 may generate a prediction block basedon information on prediction block generation received from the entropydecoding module 210 and previously decoded block or picture informationreceived from the memory 245.

As described above, like the operation of the device for encoding avideo, in performing intra prediction, when the size of the predictionunit is the same as the size of the transform unit, intra prediction maybe performed on the prediction unit based on the pixels positioned atthe left, the top left, and the top of the prediction unit. Inperforming intra prediction, when the size of the prediction unit isdifferent from the size of the transform unit, intra prediction may beperformed using a reference pixel based on the transform unit. Also,intra prediction using N×N partitioning may be used for only thesmallest coding unit.

The prediction modules 230 and 235 may include a prediction unitdetermination module, an inter prediction module, and an intraprediction module. The prediction unit determination module may receivea variety of information, such as prediction unit information,prediction mode information of an intra prediction method, informationon motion prediction of an inter prediction method, etc. from theentropy decoding module 210, may divide a current coding unit intoprediction units, and may determine whether inter prediction or intraprediction is performed on the prediction unit. By using informationrequired in inter prediction of the current prediction unit receivedfrom the device for encoding a video, the inter prediction module 230may perform inter prediction on the current prediction unit based oninformation of at least one of a previous picture or a subsequentpicture of the current picture including the current prediction unit.Alternatively, inter prediction may be performed based on information ofsome pre-reconstructed regions in the current picture including thecurrent prediction unit.

In order to perform inter prediction, it may be determined for thecoding unit which of a skip mode, a merge mode, an AMVP mode, and aninter block copy mode is used as the motion prediction method of theprediction unit included in the coding unit.

The intra prediction module 235 may generate a prediction block based onpixel information in the current picture. When the prediction unit is aprediction unit subjected to intra prediction, intra prediction may beperformed based on intra prediction mode information of the predictionunit received from the device for encoding a video. The intra predictionmodule 235 may include an adaptive intra smoothing (AIS) filter, areference pixel interpolation module, and a DC filter. The AIS filterperforms filtering on the reference pixel of the current block, andwhether to apply the filter may be determined depending on theprediction mode of the current prediction unit. AIS filtering may beperformed on the reference pixel of the current block by using theprediction mode of the prediction unit and AIS filter informationreceived from the device for encoding a video. When the prediction modeof the current block is a mode where AIS filtering is not performed, theAIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction mode inwhich intra prediction is performed based on the pixel value obtained byinterpolating the reference pixel, the reference pixel interpolationmodule may interpolate the reference pixel to generate the referencepixel of an integer pixel or less than an integer pixel. When theprediction mode of the current prediction unit is a prediction mode inwhich a prediction block is generated without interpolation thereference pixel, the reference pixel may not be interpolated. The DCfilter may generate a prediction block through filtering when theprediction mode of the current block is a DC mode.

The reconstructed block or picture may be provided to the filter module240. The filter module 240 may include the deblocking filter, the offsetcorrection module, and the ALF.

Information on whether or not the deblocking filter is applied to thecorresponding block or picture and information on which of a strongfilter and a weak filter is applied when the deblocking filter isapplied may be received from the device for encoding a video. Thedeblocking filter of the device for decoding a video may receiveinformation on the deblocking filter from the device for encoding avideo, and may perform deblocking filtering on the corresponding block.

The offset correction module may perform offset correction on thereconstructed picture based on the type of offset correction and offsetvalue information applied to a picture in performing encoding.

The ALF may be applied to the coding unit based on information onwhether to apply the ALF, ALF coefficient information, etc. receivedfrom the device for encoding a video. The ALF information may beprovided as being included in a particular parameter set.

The memory 245 may store the reconstructed picture or block for use as areference picture or block, and may provide the reconstructed picture toan output module.

As described above, in the embodiment of the present invention, forconvenience of explanation, the coding unit is used as a termrepresenting a unit for encoding, but the coding unit may serve as aunit performing decoding as well as encoding.

In addition, a current block may represent a target block to beencoded/decoded. And, the current block may represent a coding treeblock (or a coding tree unit), a coding block (or a coding unit), atransform block (or a transform unit), a prediction block (or aprediction unit), or the like depending on an encoding/decoding step.

A picture may be encoded/decoded by divided into base blocks having asquare shape or a non-square shape. At this time, the base block may bereferred to as a coding tree unit. The coding tree unit may be definedas a coding unit of the largest size allowed within a sequence or aslice. Information regarding whether the coding tree unit has a squareshape or has a non-square shape or information regarding a size of thecoding tree unit may be signaled through a sequence parameter set, apicture parameter set, or a slice header. The coding tree unit may bedivided into smaller size partitions. At this time, if it is assumedthat a depth of a partition generated by dividing the coding tree unitis 1, a depth of a partition generated by dividing the partition havingdepth 1 may be defined as 2. That is, a partition generated by dividinga partition having a depth k in the coding tree unit may be defined ashaving a depth k+1.

A partition of arbitrary size generated by dividing a coding tree unitmay be defined as a coding unit. The coding unit may be recursivelydivided or divided into base units for performing prediction,quantization, transform, or in-loop filtering, and the like. Forexample, a partition of arbitrary size generated by dividing the codingunit may be defined as a coding unit, or may be defined as a transformunit or a prediction unit, which is a base unit for performingprediction, quantization, transform or in-loop filtering and the like.

Partitioning of a coding tree unit or a coding unit may be performedbased on at least one of a vertical line and a horizontal line. Inaddition, the number of vertical lines or horizontal lines partitioningthe coding tree unit or the coding unit may be at least one or more. Forexample, the coding tree unit or the coding unit may be divided into twopartitions using one vertical line or one horizontal line, or the codingtree unit or the coding unit may be divided into three partitions usingtwo vertical lines or two horizontal lines. Alternatively, the codingtree unit or the coding unit may be partitioned into four partitionshaving a length and a width of ½ by using one vertical line and onehorizontal line.

When a coding tree unit or a coding unit is divided into a plurality ofpartitions using at least one vertical line or at least one horizontalline, the partitions may have a uniform size or a different size.Alternatively, any one partition may have a different size from theremaining partitions.

In the embodiments described below, it is assumed that a coding treeunit or a coding unit is divided into a quad tree structure or a binarytree structure. However, it is also possible to divide a coding treeunit or a coding unit using a larger number of vertical lines or alarger number of horizontal lines.

FIG. 3 is a diagram illustrating an example of hierarchicallypartitioning a coding block based on a tree structure according to anembodiment of the present invention.

An input video signal is decoded in predetermined block units. Such adefault unit for decoding the input video signal is a coding block. Thecoding block may be a unit performing intra/inter prediction, transform,and quantization. In addition, a prediction mode (e.g., intra predictionmode or inter prediction mode) is determined in a unit of a codingblock, and the prediction blocks included in the coding block may sharethe determined prediction mode. The coding block may be a square ornon-square block having an arbitrary size in a range of 8×8 to 64×64, ormay be a square or non-square block having a size of 128×128, 256×256,or more.

Specifically, the coding block may be hierarchically partitioned basedon at least one of a quad tree and a binary tree. Here, quad tree-basedpartitioning may mean that a 2N×2N coding block is partitioned into fourN×N coding blocks, and binary tree-based partitioning may mean that onecoding block is partitioned into two coding blocks. Even if the binarytree-based partitioning is performed, a square-shaped coding block mayexist in the lower depth.

Binary tree-based partitioning may be symmetrically or asymmetricallyperformed. The coding block partitioned based on the binary tree may bea square block or a non-square block, such as a rectangular shape. Forexample, a partition type in which the binary tree-based partitioning isallowed may comprise at least one of a symmetric type of 2N×N(horizontal directional non-square coding unit) or N×2N (verticaldirection non-square coding unit), asymmetric type of nL×2N, nR×2N,2N×nU, or 2N×nD.

Binary tree-based partitioning may be limitedly allowed to one of asymmetric or an asymmetric type partition. In this case, constructingthe coding tree unit with square blocks may correspond to quad tree CUpartitioning, and constructing the coding tree unit with symmetricnon-square blocks may correspond to binary tree partitioning.Constructing the coding tree unit with square blocks and symmetricnon-square blocks may correspond to quad and binary tree CUpartitioning.

Binary tree-based partitioning may be performed on a coding block wherequad tree-based partitioning is no longer performed. Quad tree-basedpartitioning may no longer be performed on the coding block partitionedbased on the binary tree.

Furthermore, partitioning of a lower depth may be determined dependingon a partition type of an upper depth. For example, if binary tree-basedpartitioning is allowed in two or more depths, only the same type as thebinary tree partitioning of the upper depth may be allowed in the lowerdepth. For example, if the binary tree-based partitioning in the upperdepth is performed with 2N×N type, the binary tree-based partitioning inthe lower depth is also performed with 2N×N type. Alternatively, if thebinary tree-based partitioning in the upper depth is performed with N×2Ntype, the binary tree-based partitioning in the lower depth is alsoperformed with N×2N type.

On the contrary, it is also possible to allow, in a lower depth, only atype different from a binary tree partitioning type of an upper depth.

It may be possible to limit only a specific type of binary tree basedpartitioning to be used for sequence, slice, coding tree unit, or codingunit. As an example, only 2N×N type or N×2N type of binary tree-basedpartitioning may be allowed for the coding tree unit. An availablepartition type may be predefined in an encoder or a decoder. Orinformation on available partition type or on unavailable partition typeon may be encoded and then signaled through a bitstream.

FIGS. 5A and 5B are diagrams illustrating an example in which only aspecific type of binary tree-based partitioning is allowed. FIG. 5Ashows an example in which only N×2N type of binary tree-basedpartitioning is allowed, and FIG. 5B shows an example in which only 2N×Ntype of binary tree-based partitioning is allowed. In order to implementadaptive partitioning based on the quad tree or binary tree, informationindicating quad tree-based partitioning, information on the size/depthof the coding block that quad tree-based partitioning is allowed,information indicating binary tree-based partitioning, information onthe size/depth of the coding block that binary tree-based partitioningis allowed, information on the size/depth of the coding block thatbinary tree-based partitioning is not allowed, information on whetherbinary tree-based partitioning is performed in a vertical direction or ahorizontal direction, etc. may be used.

In addition, information on the number of times a binary treepartitioning is allowed, a depth at which the binary tree partitioningis allowed, or the number of the depths at which the binary treepartitioning is allowed may be obtained for a coding tree unit or aspecific coding unit. The information may be encoded in a unit of acoding tree unit or a coding unit, and may be transmitted to a decoderthrough a bitstream.

For example, a syntax ‘max_binary_depth_idx_minus1’ indicating a maximumdepth at which binary tree partitioning is allowed may beencoded/decoded through a bitstream. In this case,max_binary_depth_idx_minus1+1 may indicate the maximum depth at whichthe binary tree partitioning is allowed.

Referring to the example shown in FIG. 6, in FIG. 6, the binary treepartitioning has been performed for a coding unit having a depth of 2and a coding unit having a depth of 3. Accordingly, at least one ofinformation indicating the number of times the binary tree partitioningin the coding tree unit has been performed (i.e., 2 times), informationindicating the maximum depth which the binary tree partitioning has beenallowed in the coding tree unit (i.e., depth 3), or the number of depthsin which the binary tree partitioning has been performed in the codingtree unit (i.e., 2 (depth 2 and depth 3)) may be encoded/decoded througha bitstream.

As another example, at least one of information on the number of timesthe binary tree partitioning is permitted, the depth at which the binarytree partitioning is allowed, or the number of the depths at which thebinary tree partitioning is allowed may be obtained for each sequence oreach slice. For example, the information may be encoded in a unit of asequence, a picture, or a slice unit and transmitted through abitstream. Accordingly, at least one of the number of the binary treepartitioning in a first slice, the maximum depth in which the binarytree partitioning is allowed in the first slice, or the number of depthsin which the binary tree partitioning is performed in the first slicemay be difference from a second slice. For example, in the first slice,binary tree partitioning may be permitted for only one depth, while inthe second slice, binary tree partitioning may be permitted for twodepths.

As another example, the number of times the binary tree partitioning ispermitted, the depth at which the binary tree partitioning is allowed,or the number of depths at which the binary tree partitioning is allowedmay be set differently according to a time level identifier (TemporalID)of a slice or a picture. Here, the temporal level identifier(TemporalID) is used to identify each of a plurality of layers of videohaving a scalability of at least one of view, spatial, temporal orquality.

As shown in FIG. 3, the first coding block 300 with the partition depth(split depth) of k may be partitioned into multiple second coding blocksbased on the quad tree. For example, the second coding blocks 310 to 340may be square blocks having the half width and the half height of thefirst coding block, and the partition depth of the second coding blockmay be increased to k+1.

The second coding block 310 with the partition depth of k+1 may bepartitioned into multiple third coding blocks with the partition depthof k+2. Partitioning of the second coding block 310 may be performed byselectively using one of the quad tree and the binary tree depending ona partitioning method. Here, the partitioning method may be determinedbased on at least one of the information indicating quad tree-basedpartitioning and the information indicating binary tree-basedpartitioning.

When the second coding block 310 is partitioned based on the quad tree,the second coding block 310 may be partitioned into four third codingblocks 310 a having the half width and the half height of the secondcoding block, and the partition depth of the third coding block 310 amay be increased to k+2. In contrast, when the second coding block 310is partitioned based on the binary tree, the second coding block 310 maybe partitioned into two third coding blocks. Here, each of two thirdcoding blocks may be a non-square block having one of the half width andthe half height of the second coding block, and the partition depth maybe increased to k+2. The second coding block may be determined as anon-square block of a horizontal direction or a vertical directiondepending on a partitioning direction, and the partitioning directionmay be determined based on the information on whether binary tree-basedpartitioning is performed in a vertical direction or a horizontaldirection.

In the meantime, the second coding block 310 may be determined as a leafcoding block that is no longer partitioned based on the quad tree or thebinary tree. In this case, the leaf coding block may be used as aprediction block or a transform block.

Like partitioning of the second coding block 310, the third coding block310 a may be determined as a leaf coding block, or may be furtherpartitioned based on the quad tree or the binary tree.

In the meantime, the third coding block 310 b partitioned based on thebinary tree may be further partitioned into coding blocks 310 b-2 of avertical direction or coding blocks 310 b-3 of a horizontal directionbased on the binary tree, and the partition depth of the relevant codingblocks may be increased to k+3. Alternatively, the third coding block310 b may be determined as a leaf coding block 310 b-1 that is no longerpartitioned based on the binary tree. In this case, the coding block 310b-1 may be used as a prediction block or a transform block. However, theabove partitioning process may be limitedly performed based on at leastone of the information on the size/depth of the coding block that quadtree-based partitioning is allowed, the information on the size/depth ofthe coding block that binary tree-based partitioning is allowed, and theinformation on the size/depth of the coding block that binary tree-basedpartitioning is not allowed.

A number of a candidate that represent a size of a coding block may belimited to a predetermined number, or a size of a coding block in apredetermined unit may have a fixed value. As an example, the size ofthe coding block in a sequence or in a picture may be limited to have256×256, 128×128, or 32×32. Information indicating the size of thecoding block in the sequence or in the picture may be signaled through asequence header or a picture header.

As a result of partitioning based on a quad tree and a binary tree, acoding unit may be represented as square or rectangular shape of anarbitrary size.

A coding block is encoded using at least one of a skip mode, intraprediction, inter prediction, or a skip method. Once a coding block isdetermined, a prediction block may be determined through predictivepartitioning of the coding block. The predictive partitioning of thecoding block may be performed by a partition mode (Part mode) indicatinga partition type of the coding block. A size or a shape of theprediction block may be determined according to the partition mode ofthe coding block. For example, a size of a prediction block determinedaccording to the partition mode may be equal to or smaller than a sizeof a coding block.

FIG. 7 is a diagram illustrating a partition mode that may be applied toa coding block when the coding block is encoded by inter prediction.

When a coding block is encoded by inter prediction, one of 8partitioning modes may be applied to the coding block, as in the exampleshown in FIG. 4.

When a coding block is encoded by intra prediction, a partition modePART_2N×2N or a partition mode PART_N×N may be applied to the codingblock.

PART_N×N may be applied when a coding block has a minimum size. Here,the minimum size of the coding block may be pre-defined in an encoderand a decoder. Or, information regarding the minimum size of the codingblock may be signaled via a bitstream. For example, the minimum size ofthe coding block may be signaled through a slice header, so that theminimum size of the coding block may be defined per slice.

In general, a prediction block may have a size from 64×64 to 4×4.However, when a coding block is encoded by inter prediction, it may berestricted that the prediction block does not have a 4×4 size in orderto reduce memory bandwidth when performing motion compensation.

FIG. 8 is a flowchart illustrating an inter prediction method accordingto an embodiment of the present invention.

Referring to FIG. 8, motion information of a current block is determinedS810. The motion information of the current block may include at leastone of a motion vector relating to the current block, a referencepicture index of the current block, or an inter prediction direction ofthe current block.

The motion information of the current block may be obtained based on atleast one of information signaled through a bitstream or motioninformation of a neighboring block adjacent to the current block.

FIG. 9 is a diagram illustrating a process of deriving motioninformation of a current block when a merge mode is applied to a currentblock.

If the merge mode is applied to the current block, a spatial mergecandidate may be derived from a spatial neighboring block of the currentblock S910. The spatial neighboring block may include at least one ofblocks adjacent to a top, a left, or a corner (e.g., at least one of atop left corner, a top right corner, or a bottom left corner) of thecurrent block.

Motion information of a spatial merge candidate may be set to be thesame as the motion information of the spatial neighboring block.

A temporal merge candidate may be derived from a temporal neighboringblock of the current block S920. The temporal neighboring block may meana co-located block included in a collocated picture. The collocatedpicture has a picture order count (POC) different from a current pictureincluding the current block. The collocated picture may be determined toa picture having a predefined index in a reference picture list or maybe determined by an index signaled from a bitstream. The temporalneighboring block may be determined to a block having the same positionand size as the current block in the collocated picture or a blockadjacent to the block having the same position and size as the currentblock. For example, at least one of a block including center coordinatesof the block having the same position and size as the current block inthe collocated picture or a block adjacent to a bottom right boundary ofthe block may be determined as the temporal neighboring block.

Motion information of the temporal merge candidate may be determinedbased on motion information of the temporal neighboring block. Forexample, a motion vector of the temporal merge candidate may bedetermined based on a motion vector of the temporal neighboring block.In addition, an inter prediction direction of the temporal mergecandidate may be set to be the same as an inter prediction direction ofthe temporal neighboring block. However, a reference picture index ofthe temporal merge candidate may have a fixed value. For example, thereference picture index of the temporal merge candidate may be set to‘0’.

Thereafter, the merge candidate list including the spatial mergecandidate and the temporal merge candidate may be generated S930. If thenumber of merge candidates included in the merge candidate list issmaller than the maximum number of merge candidates, a combined mergecandidate combining two or more merge candidates or a merge candidatehave zero motion vector (0, 0) may be included in the merge candidatelist.

When the merge candidate list is generated, at least one of mergecandidates included in the merge candidate list may be specified basedon a merge candidate index S940.

Motion information of the current block may be set to be the same asmotion information of the merge candidate specified by the mergecandidate index S950. For example, when the spatial merge candidate isselected by the merge candidate index, the motion information of thecurrent block may be set to be the same as the motion information of thespatial neighboring block. Alternatively, when the temporal mergecandidate is selected by the merge candidate index, the motioninformation of the current block may be set to be the same as the motioninformation of the temporal neighboring block.

FIG. 10 illustrates a process of deriving motion information of acurrent block when an AMVP mode is applied to the current block.

When the AMVP mode is applied to the current block, at least one of aninter prediction direction or a reference picture index of the currentblock may be decoded from a bitstream S1010. That is, when the AMVP modeis applied, at least one of the inter prediction direction or thereference picture index of the current block may be determined based onthe encoded information through the bitstream.

A spatial motion vector candidate may be determined based on a motionvector of a spatial neighboring block of the current block S1020. Thespatial motion vector candidate may include at least one of a firstspatial motion vector candidate derived from a top neighboring block ofthe current block and a second spatial motion vector candidate derivedfrom a left neighboring block of the current block. Here, the topneighboring block may include at least one of blocks adjacent to a topor a top right corner of the current block, and the left neighboringblock of the current block may include at least one of blocks adjacentto a left or a bottom left corner of the current block. A block adjacentto a top left corner of the current block may be treated as the topneighboring block, or the left neighboring block.

When reference pictures between the current block and the spatialneighboring block are different, a spatial motion vector may be obtainedby scaling the motion vector of the spatial neighboring block.

A temporal motion vector candidate may be determined based on a motionvector of a temporal neighboring block of the current block S1030. Ifreference pictures between the current block and the temporalneighboring block are different, a temporal motion vector may beobtained by scaling the motion vector of the temporal neighboring block.

A motion vector candidate list including the spatial motion vectorcandidate and the temporal motion vector candidate may be generatedS1040.

When the motion vector candidate list is generated, at least one of themotion vector candidates included in the motion vector candidate listmay be specified based on information specifying at least one of themotion vector candidate list S1050.

The motion vector candidate specified by the information is set as amotion vector prediction value of the current block. And, a motionvector of the current block is obtained by adding a motion vectordifference value to the motion vector prediction value 1060. At thistime, the motion vector difference value may be parsed from thebitstream.

When the motion information of the current block is obtained, motioncompensation for the current block may be performed based on theobtained motion information S820. More specifically, the motioncompensation for the current block may be performed based on the interprediction direction, the reference picture index, and the motion vectorof the current block.

As in the above example, motion compensation for the current block maybe performed based on motion information of the current block. In thiscase, a motion vector may have a precision (or resolution) of an integerpixel unit or a decimal pixel unit.

The integer pixel unit may include N integer-pel, such as aninteger-pel, 2 integer-pel, 4 integer-pel, or the like. Here, N may berepresented by a natural number of 1 or more, in particular, by anexponent of 2. The integer-pel may represent one pixel precision (i.e.,one pixel unit), the 2 integer-pel may represent twice of one pixelprecision (i.e., two pixel units), and the 4 integer-pel may representfour times of one pixel precision (i.e., four pixel units). According tothe selected integer-pel, a motion vector may be expressed in a unit ofN-pixel, and a motion compensation may be performed in a unit ofN-pixel.

The decimal pixel unit may include 1/N pel such as a half-pel, aquarter-pel, an octo-pel, or the like. Here, N may be represented by anatural number of 1 or more, in particular, by an exponent of 2. Thehalf-pel may represent ½ precision of one pixel (i.e., a half pixelunit), the quarter-pel may represent ¼ precision of one pixel (i.e., aquarter pixel unit), and the octo-pel may represent ⅛ precision of onepixel (i.e., an octo pixel unit). According to the selected decimal pel,the motion vector may be expressed in a unit of 1/N pixel, and a motioncompensation may be performed in a unit of 1/N pixel.

FIGS. 11 and 12 are diagrams illustrating a motion vector derivationmethod according to a motion vector precision of a current block. FIG.11 shows a motion vector derivation method under an AMVP mode, and FIG.12 shows a motion vector derivation method under a merge mode.

First, a motion vector precision of the current block may be determinedS1110, S1210.

A precision of a motion vector may be determined in a unit of asequence, a picture, a slice, or a predetermined block. Here, thepredetermined block may represent CTU, CU, PU, or a block of apredetermined size/shape. The CTU may mean CU of maximum size which isallowed in the encoder/decoder. If a motion vector precision isdetermined at a level higher than a block such as a sequence, a picture,or a slice, a motion compensation for the predetermined block may beperformed according to the motion vector precision determined at thehigher level. For example, a motion compensation for blocks included ina first slice may be performed using a motion vector in which aprecision is an integer-pel unit, while a motion compensation for blocksincluded in a second slice may be performed using a motion vector inwhich a precision is a quarter-pel unit.

To determine a precision of a motion vector, information for determiningthe precision of the motion vector may be signaled through thebitstream. The information may be index information,‘mv_resolution_idx’, specifying at least one of a plurality of motionvector precisions. For example, Table 1 shows motion vector precisionsaccording to mv_resolution_idx.

TABLE 1 mv_resolution_idx Motion vector pixel unit 0 Quarter pel pixelunit 1 Half pel pixel unit 2 Integer pel pixel unit 3 Octo pel pixelunit 4 2 integer pel pixel unit 5 4 integer pel pixel unit

The example shown in Table 1 is merely an example to which the presentinvention can be applied. Types and/or the numbers of motion vectorprecision candidates that can be applied to a predetermined unit may bedifferent from those shown in Table 1. A value and/or a range ofmv_resolution_idx may also differ depending on the type and/or thenumber of the motion vector precision candidates.

In another example, a motion vector precision may be derived from a unitwhich is spatially or temporally adjacent to a predetermined unit. Here,the predetermined unit may represent a picture, a slice, or a block, anda neighboring unit may represent a picture, a slice, or a block which isspatially or temporally adjacent to the predetermined unit. For example,a motion vector precision of a current block may be set equal to amotion vector precision of a block specified by index information amonga spatial neighboring block and/or a temporal neighboring block.

As another example, a motion vector precision of a current block may bedetermined adaptively according to motion information of the currentblock. For example, a motion vector precision of a current block may beadaptively determined according to whether a temporal order or a pictureorder count of a reference picture of the current block precedes acurrent picture, whether a temporal order or a picture order count of areference picture of the current block is later than a current picture,or whether a reference picture of the current block is a currentpicture.

Some of a plurality of motion vector precision candidates may beselectively used. For example, after defining a motion vector precisionset that includes at least one motion vector precision candidate, it ispossible to determine a motion vector precision by at least one motionvector precision candidate included in the motion vector precision set.

The motion vector precision set may be determined in a unit of asequence, a picture, a slice, or a block. Motion vector precisioncandidates included in the motion vector precision set may be predefinedin the encoder and the decoder. Alternatively, the motion vectorprecision set may be determined based on encoding information signaledthrough the bitstream. Here, the encoding information may be related toat least one of types and/or the number of motion vector precisioncandidates included in the motion vector resolution set. As anotherexample, the motion vector precision set may be derived from a unitspatially or temporally adjacent to a predetermined unit. Here, thepredetermined unit may represent a picture, a slice, or a block, and aneighboring unit may represent a picture, a slice, or a block spatiallyor temporally adjacent to the predetermined unit. For example, a motionvector precision set of a predetermined slice may be set equal to amotion vector precision set of a slice spatially adjacent to the slice.Alternatively, depending on a dependency between slices, a motion vectorprecision set of an independent slice may be set to a motion vectorprecision set of a dependent slice.

If the motion vector precision set is determined, at least one motionvector precision candidate included in the motion vector precision setmay be determined as a motion vector precision. To this end, indexinformation specifying at least one of motion vector precisioncandidates included in the motion vector precision set may be signaledthrough the bitstream. For example, a motion vector precision of acurrent block may be set as a candidate specified by the indexinformation among motion vector precision candidates included in themotion vector precision set.

Whether or not to use the motion vector precision set may be determinedadaptively according to a slice type, a size/shape of the current block,or motion information of the current block (e.g., a reference picture ofthe current block or a prediction direction of the current block).Alternatively, information (e.g., a flag) indicating whether the motionvector precision set is used may be signaled through the bitstream.

If the motion vector precision set is determined at a level higher thana block such as a sequence, a picture, or a slice, a motion vectorprecision of a predetermined block may be derived from the motion vectorprecision set determined at the higher level. For example, if a motionvector precision set including a quarter-pel and 2 integer-pel isdefined at a picture level, a block included in the picture may belimitedly use at least one of the quarter-pel or the 2 integer-pel.

When a multi-directional prediction is applied to a current block, aplurality of motion vectors according to the multi-directionalprediction may have different motion vector precision from each other.That is, a precision of any one of motion vectors of the current blockmay be different from a precision of another motion vector. For example,when bi-prediction is applied to the current block, a precision offorward motion vector mvL0 may be different from a precision of backwardmotion vector mvL1. Even when multi-directional prediction having morethan three direction is applied to the current block, at least one ofthe plurality of motion vectors may have a different precision fromanother. Accordingly, information for determining a motion vectorprecision may be encoded/decoded for each prediction direction of thecurrent block.

If an AMVP mode is applied to the current block and if a motion vectorprecision of each block is determined variably, a precision of a motionvector prediction value (or Motion Vector Predictor, MVP) derived from aneighboring block may be different from a motion vector precision of thecurrent block. In order to adjust the precision of the motion vectorprediction value to the motion vector precision of the current block,the motion vector prediction value may be scaled according to the motionvector precision of the current block S1120. The motion vectorprediction value may be scaled according to the motion vector precisionof the current block. A motion vector of the current block may bederived by adding a motion vector difference (MVD) to the scaled motionvector prediction value S1130.

For example, if a pixel unit of a motion vector of the neighboring blockis a quarter pel and a pixel unit of a motion vector the current blockis an integer pel, the motion vector prediction value derived from theneighboring block may be scaled in a unit of an integer pel, and amotion vector having a precision of an integer pel may be derived byadding the scaled motion vector prediction value and the motion vectordifference value. For example, the following Equation 1 shows an examplein which a motion vector is obtained by scaling the motion vectorprediction value in a unit of an integer pel.mvLX[0]=((mvpLX[0]»2)+mvdLX[0])«2mvLX[1]=((mvpLX[1]»2)+mvdLX[1])«2   [Equation 1]

In the Equation 1, mvpLX denotes a motion vector prediction value, andmvdLX denotes a motion vector difference value. In addition, mvLX[0],mvpLX[0] and mvdLX[0] represent motion vector components of a verticaldirection, and mvLX[1], mvpLX[1] and mvdLX[1] represent motion vectorcomponents of a horizontal direction.

As another example, when a pixel unit of a motion vector of aneighboring block is 2 integer-pel and a pixel unit of a motion vectorof the current block is a quarter pel, a motion vector prediction valuederived from the neighboring block may be scaled in a unit of a quarterpel, and a motion vector having a precision of a quarter pel may bederived by adding the scaled motion vector prediction value and themotion vector difference value. For example, the following Equation 2shows an example in which a motion vector is obtained when a currentpicture is used as a reference picture.mvLX[0]=((mvpLX[0]»3)+mvdLX[0])«3mvLX[1]=((mvpLX[1]»3)+mvdLX[1])«3   [Equation 2]

In Equations 1 and 2, a bit shift value used for scaling the motionvector prediction value may be adaptively determined according to ascale ratio between a motion vector precision of the current block and amotion vector precision of the neighboring block.

Unlike the example shown in FIG. 11, it is also possible to scale amotion vector generated by adding a motion vector prediction value and amotion vector difference value according to a motion vector precision ofthe current block.

A motion vector difference value may be encoded/decoded according to amotion vector precision of the current block. For example, when a motionvector precision of the current block is a quarter pel, a motion vectordifference value for the current block may be encoded/decoded in a unitof a quarter pel.

It is also possible to encode/decode a motion vector difference value ina predetermined unit regardless of a motion vector precision of thecurrent block. Here, the predetermined unit may be a fixed pixel unit(e.g., an integer pel or a quarter pel) predefined in the encoder andthe decoder, or may be a pixel unit determined at a higher level such asa picture or a slice. When a motion vector precision of the currentblock is different from a precision of the motion vector differencevalue, a motion vector of the current block may be derived by scalingthe motion vector difference value or scaling a motion vector derived byadding the scaled motion vector prediction value and the motion vectordifference value. For example, when the motion vector precision of thecurrent block is an integer pel while the motion vector difference valueis coded with a precision of a quarter pel, as shown in Equation 1, amotion vector of the current block may be derived by scaling a motionvector derived by adding the scaled motion vector prediction value andthe motion vector difference value.

Depending on a motion vector precision, an encoding/decoding method ofthe motion vector difference value may be determined differently. Forexample, if a resolution is in a unit of a decimal pixel, a motionvector difference value may be encoded/decoded by dividing it into aprefix part and a suffix part. The prefix part may represent an integerpart of a motion vector, and the suffix part may represent a fractionalpart of a motion vector. For example, the following Equation 3 shows anexample of deriving the prefix part ‘predfix_mvd’ and the suffix part‘suffix_mvd’.prefix_mvd=MVD/Nsuffix_mvd=MVD % N   [Equation 3]

In Equation 3, N may be a fixed value or may be a value that is variablydetermined according to a motion vector precision of the current block.For example, N may be proportional to the motion vector precision of thecurrent block.

If a motion vector precision of the current block is an integer pelpixel unit of two or more times, a value obtained by shifting a motionvector difference value by N may be encoded. For example, if a motionvector precision of the current block is 2 integer-pel, it is possibleto encode/decode a half of a motion vector difference value. If a motionvector precision of the current block is 4 integer-pel, it is possibleto encode/decode a quarter of a motion vector difference value. In thiscase, a motion vector of the current block may be derived by scaling adecoded motion vector difference value in accordance with the motionvector precision of the current block.

If a merge mode or a skip mode is applied to the current block and amotion vector precision of each block is determined variably, it mayoccur that a motion vector precision of the current block is differentfrom that of a spatial/temporal merge candidate block. Accordingly, amotion vector of the spatial/temporal neighboring block is scaledaccording to the motion vector precision of the current block S1220, anda scaled motion vector may be set as motion information of thespatial/temporal merging candidate S1230. For example, motion vectorsmvLX[0] and/or mvLX[1] of the spatial/temporal neighboring block arescaled according to the motion vector precision of the current block toderive the scaled motion vectors mxLXscale[0] and/or mvLXscale[1], andthe scaled motion vectors may be set as motion vectors of thespatial/temporal merge candidate.

For example, when a motion vector precision of a neighboring blockadjacent to the current block is a quarter pel and a motion vectorprecision of the current block is an integer pel, a motion vector of theneighboring block may be scaled as shown in Equation 4, and a scaledmotion vector may be set as a motion vector of a spatial mergecandidate.mvLXscale[0]=(mvLX[0]»2)«2mvLXscale[1]=(mvLX[1]»2)«2   [Equation 4]

In Equation 4, a bit shift value used for scaling a motion vector of aneighboring block may be adaptively determined according to a scaleratio between the motion vector precision of the current block and themotion vector precision of the neighboring block.

As another example, after selecting a merge candidate to be merged withthe current block (i.e., a merge candidate selected by merge index), itmay be check whether a motion vector precision of it is corresponding toa motion vector precision of the current block. If the motion vectorprecision of the selected merge candidate does not identical to themotion vector precision of the current block, a motion vector of theselected merge candidate may be scaled according to the motion vectorprecision of the current block.

A motion vector of the current block may be set equal to a motion vector(i.e., the scaled motion vector) of the merge candidate selected byindex information among merge candidates S1240.

Unlike the example shown in FIG. 12, a merge candidate for the currentblock may be determined in consideration of a motion vector precision ofa spatial/temporal neighboring block. For example, based on a result ofwhether a difference or a scale ratio between a motion vector precisionof a spatial neighboring block and a motion vector precision of thecurrent block is equal to or greater than a predetermined thresholdvalue, it may be determined that whether the spatial/temporalneighboring block is available as a merge candidate. For example, if amotion vector precision of a spatial merge candidate is 2 integer-peland a motion vector precision of the current block is a quarter-pel, itmay mean that a correlation between two blocks are not significant.Accordingly, the spatial/temporal neighboring block of which a precisiondifference with a motion vector precision of the current block isgreater than the threshold value may be set to be unavailable as a mergecandidate. That is, the spatial/temporal neighboring block can be usedas a merge candidate only when a difference between a motion vectorprecision of the spatial/temporal neighboring block and a motion vectorprecision of the current block is less than the threshold value. Thespatial/temporal neighboring block that is not unavailable as a mergecandidate may not be added to a merge candidate list.

When a difference or a scale ratio between a motion vector precision ofthe current block and a motion vector precision of the neighboring blockis less than or equal to the threshold value but both precisions aredifferent from each other, a scaled motion vector may be set as a motionvector of the merge candidate, or a motion vector of the merge candidatespecified by a merge index may be scaled as in the embodiment describedabove with reference to FIG. 12.

A motion vector of the current block may be derived from a motion vectorof the merge candidate added to the merge candidate list. If a motionvector precision of the current block is different from a motion vectorprecision of the merge candidate added to the merge candidate list,

a motion vector precision difference value may represent a differencebetween the motion vector precisions or may represent a differencebetween corresponding values each of which corresponds to a motionvector precision. Here, the corresponding value may indicate an indexvalue corresponding to a motion vector precision shown in Table 1, ormay represent a value assigned to each motion vector precision shown inTable 2. For example, in Table 2, a corresponding value assigned to aquarter pel is 2, and a corresponding value assigned to an integer pelis 3, so a difference of both precisions may be determined to be 2.

TABLE 2 Motion vector pixel unit Corresponding value Octo-pel pixel unit0 Quarter-pel pixel unit 1 Half-pel pixel unit 2 Integer-pel pixel unit3 2 integer-pel pixel unit 4 4 integer-pel pixel unit 5

The availability of the temporal/spatial neighboring block may also bedetermined using a scale ratio of motion vector precisions instead of amotion vector precision difference value. Here, the scale ratio ofmotion vector precisions may represent a ratio between both motionvector precisions. For example, a scale ratio between a quarter pel andan integer pel may be defined as 4.

Although the above-described embodiments have been described on thebasis of a series of steps or flowcharts, they do not limit thetime-series order of the invention, and may be performed simultaneouslyor in different orders as necessary. Further, each of the components(for example, units, modules, etc.) constituting the block diagram inthe above-described embodiments may be implemented by a hardware deviceor software, and a plurality of components. Or a plurality of componentsmay be combined and implemented by a single hardware device or software.The above-described embodiments may be implemented in the form ofprogram instructions that may be executed through various computercomponents and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include one of or combination ofprogram commands, data files, data structures, and the like. Examples ofcomputer-readable media include magnetic media such as hard disks,floppy disks and magnetic tape, optical recording media such as CD-ROMsand DVDs, magneto-optical media such as floptical disks, media, andhardware devices specifically configured to store and execute programinstructions such as ROM, RAM, flash memory, and the like. The hardwaredevice may be configured to operate as one or more software modules forperforming the process according to the present invention, and viceversa.

INDUSTRIAL APPLICABILITY

The present invention may be applied to electronic devices which is ableto encode/decode a video.

The invention claimed is:
 1. A method of decoding a video, the methodcomprising: determining a motion vector precision of a current block;obtaining a motion vector difference value of the current block, themotion vector difference value being scaled based on the motion vectorprecision of the current block; obtaining a motion vector predictionvalue of the current block from a motion vector predictor list;obtaining a motion vector of the current block using the motion vectorprediction value and the scaled motion vector difference value;determining a reference picture of the current block based on areference picture list; and obtaining a prediction sample of the currentblock by using the motion vector and the reference picture, wherein whenit is determined that the motion vector precision of the current blockis determined from a motion vector precision set including a pluralityof motion vector precision candidates, the motion vector precision ofthe current block is determined based on index information specifyingone of the plurality of motion vector precision candidates, wherein whenit is determined that the motion vector precision of the current blockis determined without using the motion vector precision set, the motionvector precision of the current block is determined without parsing theindex information, and wherein determination of whether the motionvector precision set is used or not is based on a flag signaled for thecurrent block.
 2. The method of claim 1, wherein a number or a type ofmotion vector precision candidates is varied according to a value ofinformation signaled for the current block.
 3. The method of claim 2,wherein a maximum bit-length of the index information is varieddepending on the value of the information.
 4. The method of claim 1,wherein the motion vector precision of the current block is determinedfurther based on whether a reference picture of the current block is acurrent picture or a picture having a POC (Picture Order Count)different from the current picture.
 5. The method of claim 1, whereinwhen it is determined that the motion vector precision of the currentblock is determined without using the motion vector precision set, themotion vector precision of the current block is determined a pre-definedvalue.
 6. A method of encoding a video, the method comprising:determining a motion vector precision of a current block; obtaining amotion vector of the current block; determining a motion vectorprediction value from a motion vector predictor list; and deriving amotion vector difference value by subtracting the motion vectorprediction value from the motion vector; determining a reference pictureof the current block based on a reference picture list; obtaining aprediction sample of the current block based on the motion vector; andencoding a scale motion vector difference value, the motion vectordifference value being scaled based on the motion vector precision ofthe current block, wherein when the motion vector precision of thecurrent block is determined from a motion vector precision set includinga plurality of motion vector precision candidates, index informationspecifying one of the plurality of motion vector precision candidates isencoded in a bitstream, wherein when the motion vector precision of thecurrent block is determined without using the motion vector precisionset, encoding the index information is skipped, and wherein a flagindicating whether the motion vector precision set is used or not isencoded in the bitstream.
 7. The method of claim 6, wherein informationfor determining a number or a type of motion vector precision candidatesis further encoded in the bitstream.
 8. The method of claim 7, wherein amaximum bit-length of the index information is determined depending on avalue of the information.
 9. The method of claim 6, wherein the motionvector precision of the current block is determined further based onwhether a reference picture of the current block is a current picture ora picture having a POC (Picture Order Count) different from the currentpicture.
 10. A non-transitory computer-readable medium for storingcompressed data associated with a video signal, the compressed datacomprising: information for a motion vector difference value of acurrent block, wherein the motion vector difference value of the currentblock is scaled based on a motion vector precision of the current block,wherein a motion vector prediction value of the current block isobtained from a motion vector predictor list, wherein a motion vector ofthe current block is obtained using the motion vector prediction valueand the scaled motion vector difference value, wherein a referencepicture of the current block is determined based on a reference picturelist, wherein a prediction sample of the current block is obtained byusing the motion vector and the reference picture, wherein when it isdetermined that the motion vector precision of the current block isdetermined from a motion vector precision set including a plurality ofmotion vector precision candidates, the motion vector precision of thecurrent block is determined based on index information specifying one ofthe plurality of motion vector precision candidates, wherein when it isdetermined that the motion vector precision of the current block isdetermined without using the motion vector precision set, the motionvector precision of the current block is determined without parsing theindex information, and wherein determination of whether the motionvector precision set is used or not is based on a flag included in thecompressed data.